I think Mira and Belle will get more popular but I don't think Mirabelle will rise too much in the future. Of course, this is only a guess because no one can predict the future. A celebrity named Mirabelle could suddenly arrive on the scene and then the name will be on everyone's radar.

i think it makes a great name! i've never actually heard it as a name before. Mia is currently in the top 10, with Mira far behind (#665 in 2013). Mila is more popular (#115). and then there's also Mina (#834). i don't see any records of the name in the top 1000 for the US before 2001, and within the last ~10 years it's climbed about 300 ranks. so i think it's likely the name will continue to rise in popularity.